Method for manufacturing non-aqueous electrolyte secondary batteries

Abstract

This invention provides a method for manufacturing a non-aqueous electrolyte secondary battery that achieves both improved accuracy in calculating internal resistance and increased efficiency in the manufacturing process. [Solution] The technology disclosed herein allows for at least 500 cm 3 A method for manufacturing a non-aqueous electrolyte secondary battery is provided, comprising: a construction step of constructing a secondary battery 100 having the above volume; an initial charging step of charging the secondary battery 100 to a state of charge (SOC) of 20% to 39%; a high-temperature aging step of raising and maintaining the secondary battery 100 in a high-temperature range; a room-temperature aging step of lowering the temperature of the secondary battery 100 from the high-temperature range to a room-temperature range and maintaining it; and a resistance testing step of calculating the internal resistance of the secondary battery 100 while maintaining the room-temperature range.

Description

[Technical Field]

[0001] This invention relates to a method for producing a non-aqueous electrolyte secondary battery. [Background technology]

[0002] Generally, the manufacturing process of non-aqueous electrolyte secondary batteries, such as lithium-ion secondary batteries, typically includes a step for testing the battery's performance. Prior art documents relating to methods for manufacturing non-aqueous electrolyte secondary batteries include Patent Documents 1 and 2. Patent documents 1 and 2 disclose an inspection method for determining the quality of battery performance by deriving the internal resistance of a battery before and after an aging process aimed at forming an SEI coating, which is performed after initial charging. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2014-225368 [Patent Document 2] Japanese Patent Publication No. 2013-152849 [Overview of the project] [Problems that the invention aims to solve]

[0004] To effectively produce an SEI coating for improving battery performance, it is necessary to pay attention to the State of Charge (SOC) value after the initial charging process. From the viewpoint of effectively forming an SEI coating, it is preferable to perform aging while the battery is charged to a high SOC. However, charging to a high SOC requires a long charging time, which causes delays in the manufacturing process. On the other hand, since the internal resistance is generally calculated using the discharge voltage, it is necessary to energize the secondary battery when deriving the internal resistance. When an energized secondary battery is energized, it generates heat due to Joule heating, which can reduce the accuracy of the internal resistance calculation. Based on the above, it can be said that it is difficult to manufacture secondary batteries without causing delays in the manufacturing process, while also accurately measuring internal resistance and providing high-quality secondary batteries. [Means for solving the problem]

[0005] To address the above issues, the method for manufacturing a non-aqueous electrolyte secondary battery disclosed herein involves at least 500 cm³ 3 The method comprises a construction step for constructing a secondary battery having the above volume, an initial charging step for charging the secondary battery to a state of charge (SOC) of 20% to 39%, a high-temperature aging step for raising and maintaining the temperature of the secondary battery in a high-temperature range, a room-temperature aging step for lowering the temperature of the secondary battery from the high-temperature range to a room-temperature range and maintaining it, and a resistance testing step for calculating the internal resistance of the secondary battery while maintaining the room-temperature range. [Brief explanation of the drawing]

[0006] [Figure 1] Figure 1 is a flowchart illustrating the manufacturing process according to one embodiment. [Figure 2] Figure 2 is a schematic perspective view showing a non-aqueous electrolyte secondary battery according to one embodiment. [Figure 3] Figure 3 is a schematic longitudinal cross-sectional view along the line II-II in Figure 2. [Figure 4] Figure 4 is a schematic perspective view showing the electrode group 20 attached to the sealing plate 14. [Figure 5] Figure 5 is a schematic perspective view of the electrode body 20a. [Figure 6] Figure 6 is a schematic diagram showing the configuration of the electrode body. [Figure 7] Figure 7 is a flowchart illustrating the manufacturing process according to one embodiment. [Figure 8] Figure 8 is a graph showing the time dependence of temperature after the charge-discharge process of a non-aqueous electrolyte secondary battery according to one embodiment. [Modes for carrying out the invention]

[0007] Preferred embodiments of the technology disclosed herein will be described below. Matters other than those specifically mentioned herein but necessary for implementing the technology disclosed herein can be understood as design matters for those skilled in the art based on prior art. The technology disclosed herein can be implemented based on the content disclosed herein and common technical knowledge in the art. Furthermore, in the drawings described herein, the same reference numerals are used to denote members and parts that perform the same function, and redundant explanations may be omitted or simplified. Also, the dimensional relationships (length, width, thickness, etc.) in each drawing do not necessarily reflect actual dimensional relationships.

[0008] In this specification, "secondary battery" refers to all energy storage devices capable of repeated charging and discharging through the movement of charge carriers between positive and negative electrodes. This concept encompasses so-called rechargeable batteries (chemical batteries) such as lithium-ion secondary batteries and sodium-ion secondary batteries, and capacitors (physical batteries) such as lithium-ion capacitors (LICs). The main constituent materials of the secondary battery according to this disclosure will be described below. Note that conventionally known constituent materials can be used for secondary batteries not described herein.

[0009] Figure 1 is a flowchart illustrating the manufacturing process according to one embodiment. Each step will be described in order below.

[0010] 1. Construction process In the construction process, a secondary battery is constructed. Figure 2 is a schematic perspective view showing a non-aqueous electrolyte secondary battery according to one embodiment. Figure 3 is a schematic longitudinal cross-sectional view along the line II-II in Figure 2.

[0011] 1.1 Secondary battery As used herein, the term "secondary battery" refers to all rechargeable power storage devices capable of repeated charge and discharge with the movement of charge carriers between the positive and negative electrodes, and includes so-called storage batteries (chemical batteries) such as lithium-ion secondary batteries and sodium-ion secondary batteries, and capacitors (physical batteries) such as lithium-ion capacitors (LICs). Hereinafter, the main constituent materials of the secondary battery according to the present disclosure will be described. For the constituent materials of the secondary battery not described herein, conventionally known materials can be used.

[0012] In the following description, the symbols L, R, F, Rr, U, and D in the drawings represent left, right, front, rear, top, and bottom, respectively, and the symbols X, Y, and Z in the drawings represent the short side direction (thickness direction), the long side direction (width direction) orthogonal to the short side direction, and the vertical direction (height direction) of the non-aqueous electrolyte secondary battery 100, respectively. However, these are merely directions for convenience of explanation and do not limit the installation form of the non-aqueous electrolyte secondary battery 100 in any way.

[0013] As shown in FIG. 3, the non-aqueous electrolyte secondary battery 100 includes a battery case 10, an electrode body group 20, a positive electrode terminal 30, a negative electrode terminal 40, a positive electrode current collector 50, and a negative electrode current collector 60. Although not shown in the figure, the non-aqueous electrolyte secondary battery 100 further includes a non-aqueous electrolyte solution here. The non-aqueous electrolyte secondary battery 100 is a lithium-ion secondary battery here.

[0014] The battery case 10 is a housing that houses the electrode body group 20. The battery case 10 has an outer shape of a flat and bottomed rectangular parallelepiped (rectangular) shape here. The material of the battery case 10 may be the same as those conventionally used and is not particularly limited. The battery case 10 is preferably made of metal, and more preferably made of, for example, aluminum, aluminum alloy, iron, iron alloy, etc. As shown in FIG. 3, the battery case 10 includes an outer package 12 having an opening 12h and a sealing plate (lid) 14 that closes the opening 12h.

[0015] As shown in Figure 2, the outer casing 12 comprises a bottom wall 12a, a pair of long side walls 12b extending from the bottom wall 12a and facing each other, and a pair of short side walls 12c extending from the bottom wall 12a and facing each other. The bottom wall 12a is substantially rectangular in shape. The bottom wall 12a faces the opening 12h. The area of ​​the short side walls 12c is smaller than the area of ​​the long side walls 12b. The long side walls 12b and short side walls 12c are examples of the first and second side walls disclosed herein. In this embodiment, the direction in which the long side walls 12b face each other is the thickness direction of the battery. The sealing plate 14 is attached to the outer casing 12 so as to close the opening 12h of the outer casing 12. The sealing plate 14 faces the bottom wall 12a of the outer casing 12. The sealing plate 14 is substantially rectangular in shape in plan view. The battery case 10 is integrated with the outer casing 12 by joining (for example, welding) a sealing plate 14 to the periphery of the opening 12h. The battery case 10 is airtight.

[0016] As shown in Figure 3, the sealing plate 14 is provided with an electrolyte injection hole 15, a gas discharge valve 17, and two terminal lead-out holes 18 and 19. The electrolyte injection hole 15 is for injecting electrolyte after the sealing plate 14 has been assembled to the outer casing 12. The electrolyte injection hole 15 is sealed by a sealing member 16. The gas discharge valve 17 is configured to rupture when the pressure inside the battery case 10 exceeds a predetermined value, thereby discharging gas from inside the battery case 10 to the outside. The terminal lead-out holes 18 and 19 are formed at both ends of the sealing plate 14 in the long side direction Y, respectively. The terminal lead-out holes 18 and 19 penetrate the sealing plate 14 in the vertical direction Z. The terminal lead-out holes 18 and 19 each have an inner diameter large enough to allow the positive electrode terminal 30 and negative electrode terminal 40 to be inserted before they are attached to the sealing plate 14 (before crimping).

[0017] The positive terminal 30 and the negative terminal 40 are fixed to the sealing plate 14. The positive terminal 30 is located on one side of the sealing plate 14 in the long side direction Y (left side in Figures 2 and 3). The negative terminal 40 is located on the other side of the sealing plate 14 in the long side direction Y (right side in Figures 2 and 3). As shown in Figure 2, the positive terminal 30 and the negative terminal 40 are exposed on the outer surface of the sealing plate 14. As shown in Figure 3, the positive terminal 30 and the negative terminal 40 extend from the inside to the outside of the sealing plate 14 through terminal lead holes 18 and 19. Here, the positive terminal 30 and the negative terminal 40 are crimped to the peripheral portion surrounding the terminal lead holes 18 and 19 of the sealing plate 14 by a crimping process. A crimped portion is formed at the end of the housing 12 on the side of the positive terminal 30 and the negative terminal 40 (upper end in Figure 3).

[0018] As shown in Figure 3, the positive terminal 30 is electrically connected to the positive tab group 23 of the electrode group 20 via the positive current collector 50 inside the casing 12. The negative terminal 40 is electrically connected to the negative tab group 25 of the electrode group 20 via the negative current collector 60 inside the casing 12. The positive terminal 30 and the negative terminal 40 are examples of terminals disclosed herein.

[0019] The positive terminal 30 is preferably made of metal, and more preferably of aluminum or an aluminum alloy. The negative terminal 40 is preferably made of metal, and more preferably of copper or a copper alloy. The negative terminal 40 may be formed by joining and integrating two conductive members. For example, the portion connected to the negative current collector 60 may be made of copper or a copper alloy, and the portion exposed on the outer surface of the sealing plate 14 may be made of aluminum or an aluminum alloy.

[0020] As shown in Figure 2, plate-shaped positive electrode external conductive members 32 and negative electrode external conductive members 42 are attached to the outer surface of the sealing plate 14. The positive electrode external conductive member 32 is electrically connected to the positive electrode terminal 30. The negative electrode external conductive member 42 is electrically connected to the negative electrode terminal 40. The positive electrode external conductive member 32 and the negative electrode external conductive member 42 are members to which busbars are attached when multiple non-aqueous electrolyte secondary batteries 100 are electrically connected to each other. The positive electrode external conductive member 32 and the negative electrode external conductive member 42 are preferably made of metal, and more preferably made of aluminum or an aluminum alloy. The positive electrode external conductive member 32 and the negative electrode external conductive member 42 are insulated from the sealing plate 14 by an external insulating member 92. However, the positive electrode external conductive member 32 and the negative electrode external conductive member 42 are not essential and can be omitted in other embodiments.

[0021] Figure 4 is a schematic perspective view showing the electrode group 20 attached to the sealing plate 14. Figure 5 is a schematic perspective view showing electrode 20a. In the non-aqueous electrolyte secondary battery 100 according to this embodiment, the electrode group 20 having a plurality of electrode bodies 20a, 20b, and 20c is housed in the battery case 10. However, the number of electrode bodies arranged inside one outer casing 12 is not particularly limited and may be two or more (multiple), or it may be just one. The detailed structure will be described later, but each of the electrode bodies 20a, 20b, and 20c has a positive electrode tab group 23 composed of a plurality of positive electrode tabs 22t and a negative electrode tab group 25 composed of a plurality of negative electrode tabs 24t. The positive electrode current collector 50 constitutes a conductive path that electrically connects the positive electrode tab group 23 and the positive electrode terminal 30. The negative electrode current collector 60 constitutes a conductive path that electrically connects the negative electrode tab group 25 and the negative electrode terminal 40. In this configuration, the electrode body 20a has a positive electrode tab group 23 at one end and a negative electrode tab group 25 at the other end.

[0022] As shown in Figure 3, the positive electrode current collector 50 comprises a positive electrode first current collector 51, which is a plate-shaped conductive member extending along the inner surface of the sealing plate 14, and a positive electrode second current collector 52, which is a plate-shaped conductive member extending along the vertical direction Z. The lower end of the positive electrode terminal 30 extends into the interior of the battery case 10 through the terminal lead-out hole 18 of the sealing plate 14 and is connected to the positive electrode first current collector 51 (see Figure 3). On the other hand, as shown in Figure 3, one end of the positive electrode second current collector 52 is connected to the positive electrode first current collector 51, and the other end is connected to the positive electrode tab group 23 of the electrode body group 20. Here, the positive electrode tab group 23 of the electrode body group 20 is bent so that the positive electrode second current collector 52 and the sides of the electrode bodies 20a, 20b, and 20c having the positive electrode tab group 23 face each other. This makes it possible to reduce the width of the positive electrode tab group 23 in the long side direction Y. As a result, the coating width in the long-side direction Y of the positive electrode active material layer 22a and the negative electrode active material layer 24a of the electrode group 20 described later can be increased, thereby enabling a higher capacity for the non-aqueous electrolyte secondary battery 100. The positive electrode first current collector 51 and the positive electrode second current collector 52 are preferably made of metal, and can be made of aluminum, aluminum alloy, nickel, stainless steel, etc.

[0023] As shown in Figure 3, the negative electrode current collector 60 comprises a negative electrode first current collector 61, which is a plate-shaped conductive member extending along the inner surface of the sealing plate 14, and a negative electrode second current collector 62, which is a plate-shaped conductive member extending along the vertical direction Z. The lower end of the negative electrode terminal 40 extends into the interior of the battery case 10 through the terminal lead-out hole 19 of the sealing plate 14 and is connected to the negative electrode first current collector 61 (see Figure 3). On the other hand, as shown in Figure 3, one end of the negative electrode second current collector 62 is connected to the negative electrode first current collector 61, and the other end is connected to the negative electrode tab group 25 of the electrode body group 20. Here, the negative electrode tab group 25 of the electrode body group 20 is bent so that the negative electrode second current collector 62 and the sides of the electrode bodies 20a, 20b, and 20c having the negative electrode tab group 25 face each other. This makes it possible to increase the capacity of the non-aqueous electrolyte secondary battery 100, similar to the configuration in which the positive electrode tab group 23 described above is bent. The negative electrode first current collector 61 and the negative electrode second current collector 62 are preferably made of metal, and can be made of copper, copper alloy, nickel, stainless steel, etc.

[0024] In the non-aqueous electrolyte secondary battery 100 according to this embodiment, various insulating members are attached between the members in order to prevent electrical conductivity between any of the members.

[0025] An insulating member is installed between the battery case 10 and the electrode group 20 to prevent electrical conductivity. Specifically, an external insulating member 92 is interposed between the positive electrode external conductive member 32 (or negative electrode external conductive member 42) and the outer surface of the sealing plate 14 (see Figure 3). This prevents the positive electrode external conductive member 32 and the negative electrode external conductive member 42 from making electrical contact with the sealing plate 14.

[0026] A gasket 90 is fitted to each of the terminal lead-out holes 18 and 19 of the sealing plate 14. This prevents the positive terminal 30 (or negative terminal 40) inserted through the terminal lead-out holes 18 and 19 from making electrical contact with the sealing plate 14.

[0027] An internal insulating member 94 is positioned between the positive electrode first current collector 51 (or negative electrode first current collector 61) and the inner surface of the sealing plate 14. This internal insulating member 94 has a plate-shaped base portion 94a interposed between the positive electrode first current collector 51 (or negative electrode first current collector 61) and the inner surface of the sealing plate 14. This prevents the positive electrode first current collector 51 or the negative electrode first current collector 61 from making electrical contact with the sealing plate 14. Furthermore, the internal insulating member 94 has a protruding portion 94b that protrudes from the inner surface of the sealing plate 14 toward the electrode group 20. This restricts the movement of the electrode group 20 in the vertical direction Z and prevents the electrode group 20 from making direct contact with the sealing plate 14.

[0028] The materials of each of the insulating members described above are not particularly limited as long as they have the required insulating properties. For example, synthetic resin materials such as polyolefin resins (e.g., polypropylene (PP), polyethylene (PE)) and fluororesins (e.g., perfluoroalkoxyalkanes (PFA), polytetrafluoroethylene (PTFE)) can be used.

[0029] 1.2 Electrode body Figure 6 is a schematic diagram showing the configuration of an electrode body. The electrode body 20 is the power generation element of the non-aqueous electrolyte secondary battery 100. As shown in Figure 6, the electrode body 20 comprises a positive electrode 22, a negative electrode 24, and a separator 26. The electrode body 20 shown in Figure 6 is a wound electrode body. This wound electrode body is created by stacking the positive electrode 22, the negative electrode 24, and the separator 26 to form a long, strip-shaped laminate, and then winding the laminate around a winding axis WL. However, the structure of the electrode body 20 is not particularly limited and may be other conventionally known structures (such as a laminated electrode body).

[0030] As shown in Figure 6, the positive electrode 22 has a positive electrode core 22c and a positive electrode active material layer 22a formed on at least one surface (in this case, both sides) of the positive electrode core 22c.

[0031] The positive electrode core 22c is strip-shaped. The positive electrode core 22c is made of a conductive metal such as aluminum, aluminum alloy, nickel, or stainless steel. In this case, the positive electrode core 22c is a metal foil, specifically an aluminum foil.

[0032] As shown in Figure 6, the positive electrode active material layer 22a is provided in a strip shape along the longitudinal direction of the strip-shaped positive electrode core body 22c. The positive electrode active material layer 22a contains a positive electrode active material capable of reversibly intercalating and releasing charge carriers. The positive electrode active material preferably contains at least one of Ni, Co, and Mn, and for example, lithium transition metal composite oxides such as lithium nickel cobalt manganese composite oxide can be used. When the total solid content of the positive electrode active material layer 22a is taken as 100% by mass, the positive electrode active material may account for approximately 80% by mass or more, typically 90% by mass or more, for example, 95% by mass or more. The positive electrode active material layer 22a may also contain optional components other than the positive electrode active material, such as conductive materials, binders, and various additives. As a conductive material, for example, carbon materials such as carbon black (e.g., acetylene black (AB)) can be used. As a binder, for example, PVdF can be used.

[0033] As shown in Figure 6, the multiple positive electrode tabs 22t protrude from the end of the electrode body 20 in the long side direction Y. The multiple positive electrode tabs 22t are also spaced apart along the longitudinal direction of the strip-shaped positive electrode 22. The shape of the tabs is rectangular in this example, but various other shapes (e.g., trapezoidal) are also possible. At least a portion of the positive electrode tab 22t has a region where the positive electrode active material layer 22a is not formed, and the positive electrode core body 22c is exposed.

[0034] As shown in Figure 6, the negative electrode 24 comprises a negative electrode core 24c and a negative electrode active material layer 24a formed on at least one surface (in this case, both surfaces) of the negative electrode core 24c.

[0035] The negative electrode core 24c is strip-shaped. The negative electrode core 24c is made of a conductive metal such as copper, copper alloy, nickel, or stainless steel. In this case, the negative electrode core 24c is a metal foil, specifically a copper foil.

[0036] The negative electrode active material layer 24a is provided in a strip shape along the longitudinal direction of the strip-shaped negative electrode core body 24c. The negative electrode active material layer 24a contains a negative electrode active material (e.g., a carbon material such as graphite, or a silicon-based material such as Si or SiO) that can reversibly absorb and release charge carriers. When the total solid content of the negative electrode active material layer 24a is taken as 100% by mass, the negative electrode active material may account for approximately 80% by mass or more, typically 90% by mass or more, for example, 95% by mass or more. The negative electrode active material layer 24a may contain optional components other than the negative electrode active material, such as a binder, a dispersant, or various additives. As a binder, for example, rubbers such as styrene-butadiene rubber (SBR) may be used. As a dispersant, for example, celluloses such as carboxymethylcellulose (CMC) may be used.

[0037] When the porosity of the negative electrode active material layer 24a is low (i.e., high density), less SEI film is generated in the initial charging process, allowing for a more accurate calculation of the resistance value in the resistance testing process before the charge-discharge process. From this viewpoint, the porosity of the negative electrode active material layer 24a is preferably 20-40%, more preferably 22-38%, and particularly preferably 25-35%.

[0038] As shown in Figure 6, the multiple negative electrode tabs 24t protrude from the end of the electrode body 20 in the long side direction Y. The multiple negative electrode tabs 24t are also spaced apart along the longitudinal direction of the strip-shaped negative electrode 24. The shape of the tabs is rectangular in this example, but various other shapes (e.g., trapezoidal) are also possible. At least a portion of the negative electrode tab 24t has a region where the negative electrode active material layer 24a is not formed, and the negative electrode core body 24c is exposed.

[0039] The separator 26 is a component that insulates the positive electrode active material layer 22a of the positive electrode 22 from the negative electrode active material layer 24a of the negative electrode 24. The separator 26 is preferably a porous resin sheet made of polyolefin resin such as polyethylene (PE) or polypropylene (PP). The separator 26 may also have a heat-resistant layer (HRL) containing an inorganic filler on the surface of the resin sheet. Examples of inorganic fillers include alumina, boehmite, aluminum hydroxide, and titania. Furthermore, it is preferable that an adhesive layer be provided on one or both sides of the separator 26. The adhesive layer improves adhesion to the positive electrode active material layer 22a or the negative electrode active material layer 24a that it contacts. The adhesive layer contains, for example, polyvinylidene fluoride (PVdF) as an adhesive component. The adhesive layer may also contain inorganic particles such as alumina and boehmite. The adhesive layer may be provided on the surface of the resin sheet, or on the surface of the HRL.

[0040] 1.3 Nonaqueous electrolyte The non-aqueous electrolyte can be the same as in the conventional method and is not particularly limited. The non-aqueous electrolyte contains, for example, a non-aqueous solvent and a supporting salt. The non-aqueous solvent contains, for example, carbonates such as ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. The supporting salt is, for example, a fluorine-containing lithium salt such as LiPF6.

[0041] 1.4 Battery Volume and Electrical Capacity The volume and electrical capacity of the non-aqueous electrolyte secondary battery relating to this disclosure should be adjusted from the following perspectives.

[0042] The internal resistance of a battery is expressed as the sum of the metal component resistance, which originates from metal components such as current collectors, and the chemical reaction resistance, which originates from the chemical reactions of the battery elements. Rechargeable batteries generate heat through repeated charging and discharging cycles due to Joule heating (Equation 1), which is the heat produced when an electric current flows through a conductor with electrical resistance. Generally, when comparing the absolute values ​​of metal component resistance and chemical reaction resistance, the former is larger. Therefore, the amount of heat generated due to Joule heating from chemical reaction resistance tends to be greater than the amount of heat generated due to Joule heating from metal component resistance. Q=EIt=(E 2 / R)t (Equation 1) Q: Joule heating [J] E: Voltage [V] I: Current [A] R: Resistance [Ω] t: Time during which the electric current was applied [s] As will be explained in more detail later, the heat generated by the secondary battery may cause an increase in the resistance of the metal components and a decrease in the chemical reaction resistance. The sum of the metal component resistance and the chemical reaction resistance after these fluctuations becomes the internal resistance after current is applied. Generally, the decrease in chemical reaction resistance is greater than the increase in metal component resistance due to temperature rise, so the internal resistance of a secondary battery tends to decrease after temperature rise. Furthermore, the proportion of chemical reaction resistance in the internal resistance is inversely proportional to the area of ​​the electrode body. For example, in small batteries with a relatively small electrode body area, the proportion of chemical reaction resistance tends to be larger compared to metal component resistance. Therefore, in small batteries with a large proportion of chemical reaction resistance, the change in chemical reaction resistance due to heat generated during charging and discharging is large, and the internal resistance can fluctuate significantly before and after charging and discharging. In other words, it is difficult to reproduce the measured value of the internal resistance after charging and discharging by measuring the internal resistance before charging and discharging.

[0043] On the other hand, the internal resistance of large batteries tends to have a smaller ratio of chemical reaction resistance to metal component resistance because the electrode area is larger compared to small batteries. Therefore, large batteries with a low ratio of chemical reaction resistance have a smaller change in chemical reaction resistance during charging and discharging, and their internal resistance does not fluctuate easily before and after charging and discharging. Based on the above, it can be understood that measuring the internal resistance before charging and discharging is equivalent to measuring the internal resistance after charging and discharging. It should be noted that the above explanation of the mechanism of action of this technology is a hypothesis and does not limit this technology.

[0044] In the secondary battery described herein, as stated above, from the viewpoint of accurately calculating the internal resistance, the volume of the secondary battery is 500 cm³. 3 The above is preferable, and 1,000 cm 3 The above is more preferable, 1,500 cm 3 The above is particularly preferable. On the other hand, if the volume of the secondary battery is too large, the room-temperature aging process described later may take a long time, so the volume of the secondary battery should be 2,500 cm³. 3 The following is preferable, 2,200 cm 3 The following is more preferable: 2,000 cm 3 The following are particularly preferable.

[0045] The secondary battery described herein is easy to enlarge from the above-mentioned perspective, and therefore it is easy to create a battery with a relatively high capacity. The capacity of the above secondary battery may be 100Ah or more, 200Ah or more, or 300Ah or more.

[0046] 2.Initial charging process In the initial charging process, the secondary battery described above is charged. During the initial charging of the battery, the electrode active material can decompose organic substances such as electrolyte components and additives that come into contact with it at a potential above a predetermined level. These decomposition products are deposited on the surface of the electrode active material as an SEI film. That is, the SEI film is composed of a mixture of decomposition products such as electrolyte components and additives. Although the SEI film does not conduct electricity, it is not a perfectly continuous film and therefore allows ions to pass through. Thus, the SEI film can stabilize and deactivate the surface of the electrode active material and suppress excessive decomposition of electrolyte components and other substances.

[0047] From the viewpoint of forming a high-quality SEI film in the initial charging process, the SOC after initial charging may be 20% or more, 25% or more, or 30% or more. On the other hand, if the SOC after initial charging is high, charging will take a long time, causing delays in the manufacturing process. Therefore, the SOC after initial charging is preferably 39% or less, more preferably 37% or less, and particularly preferably 35% or less.

[0048] 3. High-temperature aging process In the high-temperature aging process, the secondary battery is heated to a high temperature and maintained there. By performing the high-temperature aging process, excess components of the SEI film formed on the surface of the negative electrode during the initial charging process are decomposed, thereby modifying the SEI film.

[0049] From the viewpoint of suitably modifying the SEI coating, the high temperature range in the high-temperature aging process is preferably 40°C to 80°C, more preferably 50°C to 70°C, and particularly preferably 55°C to 65°C. On the other hand, from the viewpoint of improving the efficiency of the manufacturing process, the holding time in the high-temperature aging process is preferably 6 hours to 72 hours, more preferably 12 hours to 48 hours, and particularly preferably 18 hours to 24 hours.

[0050] 4. Room temperature aging process In the room temperature aging process, the secondary battery is cooled to room temperature and held there. Since the internal resistance of a battery depends on its temperature, it is difficult to accurately calculate the internal resistance when the battery is at a high temperature. This is because as the cell temperature rises, the resistance of the metal components increases, and the viscosity of the electrolyte decreases, which promotes the movement of charge carriers (lithium ions in the case of lithium-ion secondary batteries), thus reducing the resistance to chemical reactions. Therefore, the method for manufacturing a secondary battery according to this disclosure includes a room temperature aging process in which the secondary battery is cooled to room temperature and held there after the high-temperature aging process described above. Note that the above explanation of the mechanism of action of this technology is an estimate and does not limit this technology.

[0051] From the viewpoint of suitably lowering the battery temperature after the high-temperature aging process, the room temperature range for the room-temperature aging process is preferably 15°C to 30°C, more preferably 18°C ​​to 27°C, and particularly preferably 21°C to 24°C. On the other hand, from the viewpoint of improving the efficiency of the manufacturing process, the holding time for the room-temperature aging process is preferably 6 hours to 72 hours, more preferably 12 hours to 48 hours, and particularly preferably 18 hours to 24 hours.

[0052] 5. Resistance Testing Process In the resistance testing process, the internal resistance of the secondary battery is calculated while maintaining the above-mentioned room temperature range. When a secondary battery is energized, whether for charging or discharging, heat is generated according to Joule's law, and the internal resistance fluctuates depending on the amount of heat generated. However, since the secondary battery according to this disclosure is relatively large, as mentioned above, there is little change in the temperature of the battery before and after energization, and the amount of change in internal resistance is small. Therefore, even when calculating the internal resistance with discharge of the secondary battery, the internal resistance can be calculated with high accuracy.

[0053] As described above, the method for manufacturing a non-aqueous electrolyte secondary battery according to this disclosure involves charging to a relatively low SOC during the initial charging process in order to shorten the manufacturing process. Furthermore, completing the initial charging process at a low SOC also benefits the accuracy of subsequent internal resistance measurements. When the SOC is relatively low and within a predetermined range, the positive electrode does not easily absorb lithium ions during discharge, which increases the chemical reaction resistance and consequently the internal resistance. As a result, the resistance difference becomes significant, allowing for accurate measurement of the internal resistance. The method for manufacturing a non-aqueous electrolyte secondary battery according to this disclosure achieves both increased efficiency in the manufacturing process and improved accuracy in internal resistance measurement by intentionally selecting the SOC range described above.

[0054] Furthermore, in the method for manufacturing a non-aqueous electrolyte secondary battery according to this disclosure, the SOC adjustment during the calculation of internal resistance is performed in the initial charging process, and therefore, the process of adjusting the SOC again during the calculation of internal resistance is not included. This not only streamlines the manufacturing process by eliminating the unnecessary SOC adjustment process, but also improves the accuracy of the internal resistance measurement.

[0055] 6.Charging and discharging process In the charge-discharge process, the secondary battery is charged and discharged after the resistance test described above. In other words, in the method for manufacturing a non-aqueous electrolyte secondary battery according to this disclosure, the resistance test process is performed before the charge-discharge process.

[0056] ≪Rating≫ 1. Example Test The following describes test examples relating to the technology disclosed herein, but it is not intended that the technology disclosed herein is limited to these test examples.

[0057] (1) Example 1 A cathode slurry was prepared by weighing lithium nickel cobalt manganese composite oxide (NCM) as the cathode active material, polyvinylidene fluoride (PVdF) as the binder, and carbon nanotubes (CNT) as the conductive material in a mass ratio of NCM:PVdF:CNT = 97.5:1.5:1, and mixing them in N-methyl-2-pyrrolidone (NMP). This cathode slurry was applied to both sides of a long, strip-shaped cathode core (aluminum foil, 12 μm thick) and dried. This was cut to a predetermined size and rolled using a roll press to obtain a cathode sheet with a 150 μm thick cathode active material layer on both sides of the cathode core.

[0058] Next, natural graphite (C) as the negative electrode active material, styrene-butadiene rubber (SBR) as a binder, and carboxymethylcellulose (CMC) as a thickener were weighed in a mass ratio of C:SBR:CMC = 98.5:1:0.5, and mixed in water to prepare a negative electrode slurry. This negative electrode slurry was applied to both sides of a long, strip-shaped negative electrode core (copper foil, 9 μm) and dried. Through this process, a negative electrode active material layer was formed on the negative electrode core, and then rolled using a roll press to obtain a negative electrode sheet with a total thickness of 180 μm.

[0059] A three-layer structure made of PE / PP / PE, with a separator thickness of 14 μm, was prepared, and the positive electrode sheet, separator, and negative electrode sheet were stacked in that order. After attaching electrode terminals to the prepared electrode body, it was placed in a battery case together with a non-aqueous electrolyte to create a cell. Terminals were connected to the electrodes of the cell, and pre-charging was performed at 0.6C until the charge level reached 25% of the State of Charge (SOC). As the non-aqueous electrolyte, a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of EC:DMC:EMC = 3:3:4 was used, in which LiPF6 was dissolved at a concentration of 1.15 mol / L as a supporting salt.

[0060] (1) Example 1 A 200Ah secondary battery was charged with a constant current of 100A (0.5C) until its state of charge (SOC) reached 25%, as shown in Figure 1. Next, it underwent high-temperature aging treatment for 6 hours at 60°C, followed by room-temperature aging treatment for 8 hours at 25°C. After the room-temperature aging treatment, it was discharged for 10 seconds at a discharge current of 100A (0.5C). The voltages before and after discharge were V1 and V2, respectively, and the discharge current was A. The following equation (1) is used. Internal resistance=(V1-V2) / A (1) Based on this, the internal resistance (internal resistance I) of the above secondary battery before the charge and discharge process was calculated.

[0061] After calculating the internal resistance I as described above, a charge-discharge process was performed. Specifically, constant current charging was carried out at 100A (0.5C) until the charge level reached 100% (SOC) (4.3V), and then constant current discharging was carried out at 100A until the SOC reached 25% (3.6V). Then, the internal resistance after the charge-discharge process (internal resistance II) was calculated using the above formula (1), and compared with the value of internal resistance I measured before the charge-discharge process. The battery temperature at the end of the charge-discharge process was 41°C, and it took approximately 4 hours to cool down to the temperature of 25°C required for measuring internal resistance II, as shown in Figure 8.

[0062] (2) Example 2 Aside from the difference in charging capacity before and after the charge-discharge process, the secondary battery was fabricated and tested in the same manner as in Example 1.

[0063] (3) Comparative Example 1 A secondary battery with a capacity of 200Ah was prepared in the same manner as in Example 1. As shown in Figure 7, constant current charging was performed at 100A (0.5C) until the charge level reached 25% of the State of Charge (SOC). Next, high-temperature aging treatment was performed at 60°C for 6 hours, followed by room-temperature aging treatment at 25°C for 8 hours. Subsequently, as a charge-discharge process, constant current charging was performed at 100A (0.5C) until the charge level reached 100% of the SOC, followed by constant current discharge at 100A (0.5C) until the charge level reached 25% of the SOC. After the charge-discharge process, the secondary battery was cooled until its temperature dropped to 25°C, and the internal resistance II was derived in the same manner as in Example 1. In other words, in Comparative Example 1, the secondary battery was prepared and tested in the same manner as in Example 1, except that internal resistance I was not measured, and only internal resistance II was measured after the charge-discharge process. Note that the cooling after the charge-discharge process took approximately 4 hours, as shown in Figure 8.

[0064] (4) Comparative Example 2 A secondary battery with a capacity of 5Ah was prepared in the same manner as in Example 1. As shown in Figure 7, constant current charging was performed at 2.5A (0.5C) until the charge level reached 25% of the State of Charge (SOC). Next, high-temperature aging treatment was performed at 60°C for 6 hours, followed by room-temperature aging treatment at 25°C for 8 hours. Subsequently, as a charge-discharge process, constant current charging was performed at 2.5A (0.5C) until the charge level reached 100% of the SOC, followed by constant current discharge at 2.5A (0.5C) until the charge level reached 25%. After the charge-discharge process, the secondary battery was discharged at a discharge current of 2.5A (0.5C) for 10 seconds with a temperature of 25°C. The internal resistance II of the secondary battery was calculated using the above formula (1), with the voltages before and after discharge being V1 and V2, respectively, and the discharge current being A. Note that the temperature of the secondary battery after the charge-discharge process was approximately 25°C, and no intentional cooling was performed when measuring the internal resistance II. In other words, in Comparative Example 2, the secondary battery was fabricated and tested in the same manner as in Comparative Example 1, except for the battery capacity and the fact that cooling was not performed after the charge-discharge process.

[0065]

Table 1

[0066] 2. Evaluation Results From the above results, in Examples 1 and 2, the internal resistances I and II before and after the charge-discharge process were 0.5 mΩ respectively. By measuring the internal resistance before the charge-discharge process, the value of the internal resistance after the charge-discharge process could be reproduced. That is, the measurement of the internal resistance before the charge-discharge process and the measurement of the internal resistance after the charge-discharge process can be regarded as synonymous. Comparative Example 1 has a different timing for measuring the internal resistance compared to Example 1 and only measures it after the charge-discharge process. The temperature of the secondary battery after the charge-discharge process was 41°C, and the time required to cool it to 25°C for measuring the internal resistance II was about 4 hours. Comparative Example 2 has a different battery capacity compared to Comparative Example 1 and is a battery with a relatively large surface area with respect to the battery capacity. The temperature of the secondary battery after the charge-discharge process was 25°C, and cooling for alleviating the cell temperature rise due to Joule heat generated during charge-discharge was not required. This is considered to be because the surface area of the secondary battery is large with respect to the battery capacity, so heat dissipation during charge-discharge can be efficiently performed.

[0067] From the above results, when measuring the internal resistance of a secondary battery with a relatively large electrode body area before the charge-discharge process after the completion of the normal temperature aging process, since cooling for alleviating the temperature rise of the secondary battery due to Joule heat generated during charge-discharge is not required, it was confirmed that the manufacturing process time can be shortened. In addition, in a secondary battery with a relatively large surface area of the secondary battery with respect to the battery capacity as in Comparative Example 2, the secondary battery that has generated heat due to charge-discharge can be efficiently heat-dissipated, and there is no problem in measuring the internal resistance after the charge-discharge process, so it is outside the scope of the technical idea according to the present disclosure.

[0068] In the above-described embodiment, the manufacturing method of the non-aqueous electrolyte secondary battery is at least 500 cm 3The method comprises an assembly step for constructing a secondary battery having the above volume, an initial charging step for charging the secondary battery to a state of charge (SOC) of 20% to 39%, a high-temperature aging step for raising and maintaining the temperature of the secondary battery in a high-temperature range, a room-temperature aging step for lowering the temperature of the secondary battery from the high-temperature range to a room-temperature range and maintaining it, and a resistance testing step for calculating the internal resistance of the secondary battery while maintaining the room-temperature range.

[0069] In this method of manufacturing non-aqueous electrolyte secondary batteries, the secondary batteries are relatively large, and the state of charge (SOC) after initial charging is a relatively low predetermined value. Therefore, the effect of Joule heating before and after energization is less pronounced, and the internal resistance can be calculated accurately. In addition, the manufacturing process can be made more efficient by shortening the charging time and the discharge time during internal resistance measurement.

[0070] In the embodiment described above, the internal resistance is measured before the charging and discharging process. This prevents the device from being affected by the heat generated due to Joule heating during the charging and discharging process, allowing for accurate calculation of the internal resistance.

[0071] In the above-described embodiment, the volume of the secondary battery is relatively large, and the proportion of metal component resistance in the internal resistance is relatively large, resulting in less heat generation due to Joule heating associated with current flow. This allows for highly accurate calculation of internal resistance and enables efficient manufacturing by minimizing the time required for current flow during calculation.

[0072] In the embodiments described above, the manufacturing process can be made more efficient because the SOC after the initial charging process is relatively low. Furthermore, because the SEI film generated after the initial charging process is relatively small, the accuracy of the internal resistance calculation can be improved.

[0073] In the above-described embodiment, it is possible to suitably manufacture large batteries with a relatively large volume. This allows for the suitability of increasing the capacity of secondary batteries.

[0074] In the embodiment described above, the State of Charge (SOC) after the initial charging process is adjusted to a predetermined value. This suppresses the decrease in measurement accuracy of the internal resistance of the secondary battery caused by Joule heating, and also improves the efficiency of the manufacturing process by shortening the charging time.

[0075] In the above-described embodiment, the SEI coating formed after the initial charging process can be suitably modified by adjusting the temperature at which the aging process is carried out.

[0076] In the above-described embodiment, by adjusting the temperature at which the room-temperature aging process is carried out, the secondary battery after high-temperature aging can be appropriately cooled, and the internal resistance can be measured with high accuracy.

[0077] In the above-described embodiment, the SEI coating formed after the initial induction charging process can be suitably modified by adjusting the time for which the high-temperature aging process is carried out.

[0078] In the embodiment described above, by adjusting the time spent on the room-temperature aging process, the secondary battery after the high-temperature aging process can be cooled down appropriately, allowing for accurate measurement of its internal resistance.

[0079] The technologies disclosed herein have been described in detail above. Unless otherwise specified, the embodiments and other details mentioned herein do not limit the present invention. Furthermore, the technologies disclosed herein can be modified in various ways, and each component and each process mentioned herein may be omitted or combined as appropriate, unless no particular problems arise. This specification also includes the disclosures described in the following sections.

[0080] Section 1: At least 500cm 3 A construction process for constructing a secondary battery having the above volume, The initial charging process involves charging the secondary battery to a state of charge (SOC) of 20% to 39%, A high-temperature aging process in which the secondary battery is heated to a high temperature range and maintained there, A room temperature aging process for cooling down the secondary battery from the high-temperature range to the room temperature range and maintaining it there, A resistance testing step for calculating the internal resistance of the secondary battery while maintaining the aforementioned room temperature range, A method for manufacturing a non-aqueous electrolyte secondary battery, comprising the features described above.

[0081] Section 2: A method for manufacturing a non-aqueous electrolyte secondary battery according to item 1, further comprising the step of charging and discharging the secondary battery after the resistance test.

[0082] Section 3: The volume of the aforementioned secondary battery is 500 cm³. 3 ~2500cm 3 A method for producing a non-aqueous electrolyte secondary battery as described in item 1 or 2.

[0083] Section 4: A method for manufacturing a non-aqueous electrolyte secondary battery according to any one of items 1 to 3, wherein the porosity of the negative electrode active material layer is 20% to 40%.

[0084] Section 5: A method for manufacturing a non-aqueous electrolyte secondary battery according to any one of items 1 to 4, wherein the capacity of the secondary battery is 100 Ah or more.

[0085] Item 6: A method for manufacturing a non-aqueous electrolyte secondary battery according to any one of items 1 to 5, wherein the initial charging step is to charge the SOC to 20% to 100%.

[0086] Section 7: The method for manufacturing a non-aqueous electrolyte secondary battery according to any one of claims 1 to 6, wherein the high-temperature range is 40°C to 80°C.

[0087] Section 8: A method for manufacturing a non-aqueous electrolyte secondary battery according to any one of claims 1 to 7, wherein the room temperature range is 15°C to 30°C.

[0088] Section 9: A method for manufacturing a non-aqueous electrolyte secondary battery according to any one of claims 1 to 8, wherein the holding time for the high-temperature aging step is 6 to 72 hours.

[0089] Section 10: A method for manufacturing a non-aqueous electrolyte secondary battery according to any one of items 1 to 9, wherein the holding time for the aforementioned room temperature aging step is 6 hours to 72 hours. [Explanation of symbols]

[0090] 10 Battery Case 12 Exterior 14 Sealing plate 20 Electrode group 20a, 20b, 20c electrode body 22 Positive electrode 22a Cathode active material layer 22c positive electrode core 22t positive electrode tab 24 Negative electrode 24a Negative electrode active material layer 24c negative electrode core 24t negative electrode tab 26 Separators 30 Positive terminal 40 Negative terminal 50 Positive electrode current collector 60 Negative electrode current collector 100 Nonaqueous electrolyte secondary battery

Claims

1. At least 500 cm ３ A construction process for constructing a secondary battery having the above volume, The initial charging process involves charging the secondary battery to a state of charge (SOC) of 20% to 39%, A high-temperature aging process for raising the temperature of the secondary battery to a high-temperature range and maintaining it there, A room temperature aging process for cooling down the secondary battery from the high-temperature range to the room temperature range and maintaining it there, A resistance testing step in which the internal resistance of the secondary battery is measured while maintaining the aforementioned room temperature range, A method for manufacturing a non-aqueous electrolyte secondary battery, comprising the features described above.

2. A method for manufacturing a non-aqueous electrolyte secondary battery according to claim 1, further comprising the step of charging and discharging the secondary battery after the resistance test.

3. The volume of the aforementioned secondary battery is 500 cm³. ３ ~2500cm ３ The method for producing a non-aqueous electrolyte secondary battery according to claim 1 or 2.

4. A method for manufacturing a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the porosity of the negative electrode active material layer is 20% to 40%.

5. The method for manufacturing a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the electrical capacity of the secondary battery is 100 Ah or more.

6. The method for manufacturing a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the initial charging step charges the SOC to 20% to 100%.

7. The method for manufacturing a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the high-temperature range is 40°C to 80°C.

8. The method for manufacturing a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the room temperature range is 15°C to 30°C.

9. The method for manufacturing a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the holding time for the high-temperature aging step is 6 hours to 72 hours.

10. The method for manufacturing a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the holding time for the room temperature aging step is 6 hours to 72 hours.

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